At present, color recording techniques such as by electrophotography, ink jet process, heat-sensitive transfer process or the like are known.
The heat-sensitive transfer recording process can be deemed to be of greater advantage than other processes because the equipment for use in such a process are easy to maintain and operate, and the equipment itself and the materials to be consumed are inexpensive.
The heat-sensitive transfer processes include a melt process and a sublimating process. In the melt process, a transfer sheet comprising a heat-meltable ink layer formed on a base film is heated by a thermal head so that the ink imagewise melt transferred to transfer images to a recording material. In the sublimating process, a transfer sheet comprising a coloring material layer containing a sublimable dye formed on a base film is heated by a thermal head so that the dye is imagewise sublimated and transfered to form an image on a recording material. In the sublimating process, the amount of the dye to be sublimated can be easily controlled by properly altering the energy applied to the thermal head. Thus, the sublimating process can easily provide records with a sufficient gradation. Accordingly, the sublimating process is particularly favorable for full-color recording.
In order to provide a cyan color record in the sublimating heat-sensitive transfer process, a transfer material comprising a coloring material layer containing a cyan dye may be used. However, conventional cyan color transfer materials are deficient in their properties. It has therefore been desired to develop improved cyan color transfer materials.
The dye to be incorporated in such cyan color transfer materials is required to satisfy various requirements described hereinafter.
Particularly, to be sutiable for a sublimating type heat-sensitive transfer process, a dye is required to be easily transferred under the normal operating conditions of the thermal recording head. Such a dye is also required to stand the normal temperature conditions of the heat-sensitive recording head without thermal decomposition. In order to provide an excellent color reproduction capability, such a dye is required to have a proper color hue and a great molecular extinction coefficient. Moreover, such a dye should be fast to heat, light, moisture, chemicals, and the like. Furthermore, such a dye should be easily synthesized. Furthermore, such a dye should be well adapted to be incorporated in an ink composition.
However, dyes which have been heretofore proposed have various deficiencies. For example, anthraquinone dyes as described in JP-A-60-151097 and 60-151098 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") are disadvantageous in that they have a poor color hue. Indoaniline dyes as described in JP-A-61-22993 and British Patent 2,161,824 are disadvantageous in that they are poor in fastness to heat and light.